Method of forming a reinforced foam-filled composite stringer

ABSTRACT

A method and apparatus for manufacturing a composite stringer. A composite material and foam are laid up onto a tool in the form of a stringer. The foam has a plurality of structural members within the foam. The plurality of structural members has a number of orientations to resist a number of loads. The composite material, the foam in the form of the stringer, and the plurality of structural members are cured to form the composite stringer.

BACKGROUND INFORMATION

1. Field

The present disclosure relates generally to aircraft parts and, inparticular, to aircraft stringers. Still more particularly, the presentdisclosure relates to a method and apparatus for a composite stringer.

2. Background

Aircraft generally include an airframe, which may be regarded as anunderlying skeleton to which skin panels are attached to form a smoothaerodynamic outer surface. The wings also include an underlyingstructure covered with skin panels. Typically, skin panels are light andthin to minimize the weight of the aircraft and increase its payload andrange. Since skin panels are thin, they are generally flexible andrequire stiffening to prevent undesired movement, flexing, and vibrationduring flight.

Hat stringers have been used for decades in the aerospace industry forstiffening metal fuselage sections and metal wing skins on bothcommercial and military aircraft. These stringers are composed of thinmetal panels with acute angles that result in a trapezoidal shape,rectangular shape, semi-circular shape, or some other suitable shape.Relatively simple metal-forming techniques are used to bend the metalinto the acute angles required for this shape. These metal-formingtechniques include brake forming or rolling the metal into the hatstringer shape. These techniques allow the production of hat stringerswith tight, constant angular bends and straight or flat legs.

In manufacturing composite hat stringers, a hat stringer may be placedon a fuselage skin in which the interior of the hat stringer has ahollow section that is formed with a bladder. These bladders areinserted into the composite stringer prior to performing curingprocesses. A curing process is a process that toughens or hardens apolymer material in the composite stringer. These bladders are inflatedto support the internal structure of the composite stringer during thecuring process in an oven or autoclave.

One drawback with the use of bladders is that, in some cases, a bladdermay deflate inside of a composite stringer during the curing process.This deflation may result in an improperly formed composite stringerthat may not work properly. As a result, the composite stringer isdiscarded and a new stringer is manufactured. The problems that mayoccur with deflation of a bladder during curing of a composite stringerinclude, for example, an improper shape for the stringer, ply movement,ply wrinkling, or porosity.

Therefore, it would be advantageous to have a method and apparatus thatovercomes the above-described problems.

SUMMARY

In one advantageous embodiment, a method is present for manufacturing acomposite stringer. A composite material and foam are laid up onto atool in the form of a stringer. The foam has a plurality of structuralmembers within the foam. The plurality of structural members has anumber of orientations to resist a number of loads. The compositematerial, the foam in the form of the stringer, and the plurality ofstructural members are cured to form the composite stringer.

In another advantageous embodiment, a method is present for forming acomposite part. A foam core having a plurality of structural members isformed. The plurality of structural members has a number of orientationsto resist a number of loads. The composite part is formed with a channelin which the foam core is located.

In yet another advantageous embodiment, a method is present formanufacturing a plurality of composite stringers. Composite material andfoam is laid up with a plurality of structural members within the foamonto a plurality of tools to form a plurality of composite stringers.The plurality of structural members has a number of orientations toresist a number of loads. The plurality of composite stringers is placedon a single tool. A skin ply is placed over the plurality of compositestringers to form a structure, and the structure is cured.

In yet another advantageous embodiment, an apparatus comprises acomposite part having a channel, foam, and a plurality of structuralmembers. The plurality of structural members has a number oforientations to resist a number of loads.

The features, functions, and advantages can be achieved independently invarious embodiments of the present disclosure or may be combined in yetother embodiments in which further details can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the advantageousembodiments are set forth in the appended claims. The advantageousembodiments, however, as well as a preferred mode of use, furtherobjectives, and advantages thereof, will best be understood by referenceto the following detailed description of an advantageous embodiment ofthe present disclosure when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a diagram illustrating an aircraft manufacturing and servicemethod in accordance with an advantageous embodiment;

FIG. 2 is a diagram of an aircraft in which an advantageous embodimentmay be implemented;

FIG. 3 is a diagram of a portion of a fuselage in accordance with anadvantageous embodiment;

FIG. 4 is a portion of a fuselage section in accordance with anadvantageous embodiment;

FIG. 5 is a diagram illustrating components used to manufacture a foamstiffened composite stringer in accordance with an advantageousembodiment;

FIG. 6 is a diagram illustrating an example lay up of compositematerials on an inside mold line tool for a composite stringer inaccordance with an advantageous embodiment;

FIG. 7 is a diagram illustrating an example lay up of compositematerials on an outside mold line tool for a composite stringer inaccordance with an advantageous embodiment;

FIG. 8 is a cross-sectional view of a foam-filled stringer withstructural members in accordance with an advantageous embodiment;

FIG. 9 is a diagram illustrating a cross-sectional view of a compositestringer in accordance with an advantageous embodiment;

FIG. 10 is a diagram of a composite stringer in accordance with anadvantageous embodiment;

FIG. 11 is a diagram illustrating a composite stringer in accordancewith an advantageous embodiment;

FIG. 12 is a flowchart of a process for manufacturing a composite partin accordance with an advantageous embodiment; and

FIG. 13 is a flowchart of a process for manufacturing a compositestringer with a foam core in accordance with an advantageous embodiment.

DETAILED DESCRIPTION

Referring more particularly to the drawings, embodiments of thedisclosure may be described in the context of aircraft manufacturing andservice method 100 as shown in FIG. 1 and aircraft 200 as shown in FIG.2. Turning first to FIG. 1, a diagram illustrating an aircraftmanufacturing and service method is depicted in accordance with anadvantageous embodiment. During pre-production, exemplary aircraftmanufacturing and service method 100 may include specification anddesign 102 of aircraft 200 in FIG. 2 and material procurement 104.

During production, component and subassembly manufacturing 106 andsystem integration 108 of aircraft 200 in FIG. 2 takes place.Thereafter, aircraft 200 in FIG. 2 may go through certification anddelivery 110 in order to be placed in service 112. While in service by acustomer, aircraft 200 in FIG. 2 is scheduled for routine maintenanceand service 114, which may include modification, reconfiguration,refurbishment, and other maintenance or service.

Each of the processes of aircraft manufacturing and service method 100may be performed or carried out by a system integrator, a third party,and/or an operator. In these examples, the operator may be a customer.For the purposes of this description, a system integrator may include,without limitation, any number of aircraft manufacturers andmajor-system subcontractors; a third party may include, withoutlimitation, any number of venders, subcontractors, and suppliers; and anoperator may be an airline, leasing company, military entity, serviceorganization, and so on.

With reference next to FIG. 2, a diagram of an aircraft is depicted inwhich an advantageous embodiment may be implemented. In this example,aircraft 200 is produced by aircraft manufacturing and service method100 in FIG. 1. Aircraft 200 has wings 202 and 204 attached to fuselage206. Aircraft 200 also has engine 208, engine 210, and tail 212. Section214 is an example of a section of fuselage 206 in which an advantageousembodiment may be implemented.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of aircraft manufacturing and service method 100 inFIG. 1. For example, components or subassemblies produced in componentand subassembly manufacturing 106 in FIG. 1 may be fabricated ormanufactured in a manner similar to components or subassemblies producedwhile aircraft 200 is in service 112 in FIG. 1.

Also, one or more apparatus embodiments, method embodiments, or acombination thereof may be utilized during production stages, such ascomponent and subassembly manufacturing 106 and system integration 108in FIG. 1, for example, without limitation, by substantially expeditingthe assembly of or reducing the cost of aircraft 200. Similarly, one ormore of apparatus embodiments, method embodiments, or a combinationthereof may be utilized while aircraft 200 is in service 112 or duringmaintenance and service 114 in FIG. 1.

The different advantageous embodiments recognize that other materialsmay be used in place of an inflatable bladder to form a cavity orchannel within a composite part.

The advantageous embodiments recognize that hard tools may be used toform a composite stringer. These hard tools may be made from materialssuch as, for example, silicone rubber or machined aluminum. Thedifferent advantageous embodiments, however, realize that in variouscomponents such as fuselage barrels, wing skins, and door panels, theshape of the composite stringers may have complex contours making thesetypes of tooling options difficult or impossible to remove for longpanels to form a hollow composite stringer. A long panel may be, forexample, a panel that is around 50 feet to around 100 feet long.

The different advantageous embodiments recognize that an alternativematerial that may be used is foam in place of hard tools to help shapethe composite stringer. Further, this type of material may remain in thestringer as part of the structure. Foam filled composite stringers havenumerous advantages over conventional hollow composite stringers. Theseadvantages include, for example, increased impact resistance, improvedstructural properties, acoustical deadening, moisture infiltrationreduction, simplified fabrication, reduced handling needs, eliminationof a need for noodles (radius support fillers) or wrap plies, reducedtendency to bow out when placed over padups, and flow time reductions.

The different advantageous embodiments also recognize that currentstringers with foam may be impractical. The different advantageousembodiments recognize that selecting a foam with a high enoughcompressible strength to avoid an improper shape for a compositestringer may require foam having higher weight than desired. Thedifferent advantageous embodiments also recognize that a thicker wallfor the stringer also may be used. This solution also may increase theweight of the composite stringer. Thus, the different advantageousembodiments recognize that it would be advantageous to have a method andapparatus for manufacturing a composite stringer filled with foam in amanner that reduces the weight of the composite stringer.

The different advantageous embodiments provide a method and apparatusfor manufacturing a composite stringer. A composite material and foam islaid up onto a tool in the form of a stringer. The foam has a pluralityof structural members located within the foam. The plurality ofstructural members has a number of orientations to resist a number ofloads generated by the composite material. A number, as used herein,refers to one or more items. For example, a number of orientations isone or more orientations. The composite material, the foam in the formof the stringer, and the plurality of structural members are cured toform the composite stringer.

With reference now to FIG. 3, a diagram of a portion of a fuselage isdepicted in accordance with an advantageous embodiment. In this example,section 214 of fuselage 206 may employ composite stringers to stiffenskin panels 300 within section 214 of fuselage 206.

With reference now to FIG. 4, a portion of a fuselage section isdepicted in accordance with an advantageous embodiment. In this example,section 400 is a cross section of fuselage section 214 taken along lines4-4 from FIG. 3. One or more skin panels may be assembled to form a skinof a structure. As can be seen in this view, section 400 has fuselageskin 402 on frame members 404 and 406. Fuselage skin 402 may bestiffened through the use of stringers 408, 410, 412, 414, 416, 418,420, 422, 424, 426, 428, 430, 432, 434, and 436.

With reference now to FIG. 5, a diagram illustrating components used tomanufacture a foam stiffened composite stringer is depicted inaccordance with an advantageous embodiment. In these examples, lay uptool 500, shape forming tool 502, foam tool 504, structural member tool505, mold tool 506, and autoclave/oven 508 are used in these examples tomanufacture composite part 510.

Composite part 510 may be a stringer, such as those illustrated in FIG.4. The illustrative examples for the different advantageous embodimentsdescribed herein are directed towards a composite part in the form of astringer. Of course, the different advantageous embodiments may beemployed with other types of composite parts other than stringers. Thedifferent advantageous embodiments may be applied to composite partssuch as, for example, without limitation, a truss structure, a flutedstructure, a hatch structure, a beaded core structure, and/or othersuitable structures.

Composite material 512 and foam 514 are formed on fuselage skin 516 inthese examples. Composite material 512 has channel 518 in which foam 514is located. Channel 518 may extend all the way through composite part510, from one end of composite part 510 to another end of composite part510. In other embodiments, channel 518 may only extend partially throughcomposite part 510. Structural members 522 are located within foam 514and may resist a number of loads generated by composite material 512.

Composite material 512 may be processed using lay up tool 500 and shapeforming tool 502. Lay up tool 500 is used in this example to stack orlay up plies of composite material 512 into a layer for composite part510. The layer may also be referred to as a flat charge. The flat chargeis processed by shape forming tool 502 to form the desired shape forcomposite part 510. In these examples, composite part 510 is a compositestringer with a hat shape.

Lay up tool 500 may be implemented using various composite materialprocessing tools such as, for example, an M. Torres lay up, which is atape layer machine available from M. Torres. Another example of amachine that may be used for lay up tool 500 is Access-Atlas, which is acomposite working machine, which is available from Forest-Line. Shapeforming tool 502 may be implemented using a machine or tool that iscapable of forming composite material into the desired shape. A formingdie or press may be used to implement shape forming tool 502. An exampleof a press that may be used is a composite spar drape forming machine.

Foam 514 is a foam core located within channel 518. Foam 514 is formedby foam tool 504 in these examples. In these examples, foam 514 may bemade from various materials. Foam 514 also is referred to as a polymeror cellular polymer foam. Foam 514 may be manufactured from a two-phasedmixture in which gases, bubbles, or cells are disbursed within a solidpolymeric resin. These bubbles or cells may be created through chemicaladditives. For example, a gas may be created by polymerization reactionor thermal decomposition. These cells also may be created within theresin through physical blowing agents, such as inert gases. Cellscreated in this manner may be open and loosely interconnected or closedand detached.

When a higher percentage of closed cells are present in a foam, thedensity of the foam is higher as well as the weight. In these examples,foam 514 may be made through a number of different methods including,for example, combining blowing agents in liquid resin and then curingthe mixture in a mold, through extrusion, compression or injectionmolding, or solid-state fabrication.

Foam 514 may be implemented with any foam that can remain intact duringa curing process. Examples of foams that may be used for foam 514include, for example, without limitation, Last-A-Foam containingpolyisocyanurate, which is available from General Plastics; Aircellcontaining aromatic polyester, which is available from Polyumac;Performa-H containing polyimide which is available from GFT Corporation;Corecell containing styrene acrylo-nitrile, which is available fromGurit; RIMA containing polymethacryllmide, which is available fromDegussa/Rohacell; Airex containing polyetherimide, which is availablefrom Alcan/Baltek; PrimoSpire/Parmax containing polyphenylenes, which isavailable from Solvay/Mississippi Poly Tech; LCP containingpolyetherether-ketone, which is available from Wright Materials ResearchCompany; Zotek containing polyvinylidene fluoride, which is availablefrom ZoteFoams; Elfoam containing polyisocyanurate, which is availablefrom Elliott Company; and Divinycell HT containing poly vinyl chloride,which is available from Diab.

Foam 514 may be formed with structural members 522 in place orstructural members 522 being inserted into foam 514 afterwards. Foamtool 504 may be implemented using any machine that is capable of formingfoam 514. An example of a machine that may be used to implemented foamtool 504 is a TVZ series machine, such as TVZ 4P, manufactured byTeubert.

Structural members 522 may be any component that is capable of providingreinforcement to resist loads generated by composite material 512 duringthe curing process within autoclave/oven 508. Structural members 522 maycomprise at least one of a number of pins, a number of tubes, a numberof rods, and a number of any other suitable structural members. Thenumber of tubes and the number of rods may be any shape such as, forexample, rectangular, square, circular, triangular, or some othersuitable shape. Further, these structural members may be hollow orsolid.

As used herein, the phrase “at least one of”, when used with a list ofitems, means that different combinations of one or more of the items maybe used and only one of each item in the list may be needed. Forexample, “at least one of item A, item B, and item C” may include, forexample, without limitation, item A or item A and item B. This examplealso may include item A, item B, and item C or item B and item C. Inother words, one or more of each type of structural member may be usedin some advantageous embodiments rather than only using a single type ofstructural member.

Structural member tool 505 may be used to insert structural members 522into foam 514. For example, when structural members 522 take the form ofpins, structural member tool 505 may be a press with ultrasonicvibration. Of course, other types of tools may be used depending on theparticular type of structural member. Examples of presses that may beused include the Sureweld 20, Sureweld 35, and Sureweld 70 models madeby Sonobond Ultrasonics, Inc., as well as the 2000x series models madeby Branson Ultrasonics Corporation, that may be mounted on a three-axisgantry.

Further, structural members 522 are selected from materials that may becapable of resisting a compressive load applied onto composite part 510without allowing foam 514 to collapse. Structural members 522 may beconstructed from various materials. For example, the material may bealuminum, steel, carbon, titanium, a metal alloy, a ceramic material, orsome other suitable material.

In these examples, structural members 522 have parameters such asorientation 524 and density 526. Orientation 524 is the orientation ofeach structural member within structural members 522. Orientation 524may have one or more orientations depending on the particularimplementation. In these examples, orientation 524 may be oriented toresist applied loads to composite part 510 during the curing processthat may otherwise cause a collapse of foam 514 within compositematerial 512.

Orientation 524 also may be selected to resist loads that may be appliedto composite part 510 in use. These orientations may be described byangles with respect to a particular surface of composite part 510.Density 526 is the number of structural members 522 located in an area.The densities may vary depending on the particular design. Further, thedensity may be uniform within foam 514 or may be non-uniform. Forexample, an area within foam 514 may have a higher density of structuralmembers 522 if a higher load may be anticipated for that particulararea.

Composite part 510 on fuselage skin 516 and mold tool 506 are placedinto autoclave/oven 508 to perform a curing process. Mold tool 506 maybe, for example, an inside mold line tool or an outside mold line tool,depending on the implementation. The temperatures in autoclave/oven 508may be around 350 degrees Fahrenheit.

Additionally, autoclave/oven 508 also may introduce pressure inperforming the curing process for composite part 510. The pressure maybe, for example, around 100 pounds per square inch. The heating causespolymer materials, such as resins, in composite material 512 to flow.When polymers harden, composite part 510 is considered to be cured inthese examples. The use of structural members 522 may prevent foam 514from collapsing within composite part 510 during the curing process.Structural members 522 also may aid foam 514 in resisting compressiveloads that may be applied during the curing process.

Autoclave/oven 508 may be implemented using any autoclave/oven ormachine that is capable of curing composite components. An Anchorautoclave from Anchor Autoclave Systems, and an autoclave available fromTaricco Corporation are examples of autoclaves that may be used toimplement autoclave/oven 508. Composite part 510 also may be cured usingother mechanisms other than autoclave/oven 508 in other embodiments. Forexample, electron beam curing may be used to cure composite material512.

After curing has occurred, composite part 510 is removed fromautoclave/oven 508. In these examples, foam 514 may provide features andadvantages as described above with respect to having foam located insidecomposite part 510. Composite part 510 may provide a number of differentfeatures in addition to a lighter weight as compared to composite partscreated with currently used methods. For example, composite part 510also may act as a noise attenuator and/or structural vibration dampener.

Further, composite part 510 also may provide increased structuralstabilization. For example, buckling and crippling may be less likely tooccur with composite part 510. Further, composite part 510 also mayblock the ingress of liquids into composite part 510. The use ofstructural members 522 may provide greater resistance to compressiveforces that may be applied to composite part 510 in use.

The illustration of the components used to manufacture a compositestringer with a foam core is not meant to imply physical orarchitectural limitations to the manner in which composite parts withfoam cores may be manufactured. Other advantageous embodiments mayinclude other components in addition to or in place of the onesillustrated in these examples. For example, the different toolsillustrated may be computer controlled tools connected to a computer ornetwork.

Turning now to FIG. 6, a diagram illustrating an example lay up ofcomposite materials on an inside mold line tool for a composite stringeris depicted in accordance with an advantageous embodiment. In thisexample, composite stringer 600 includes composite material 602 and foam604. Composite material 602 is laid up over foam 604. Foam 604 is placedinto inside mold line tool 606. Then fuselage skin 608 is placed or laidup onto composite material 602, foam 604, and inside mold line tool 606.Caul 610 is placed against fuselage skin 608 in these examples.

Foam 604 has structural members 612. In these illustrative examples,structural members 612 may be placed into foam 604 prior to being shapedfor use in composite stringer 600. In other advantageous embodiments,foam 604 may be formed around structural members 612. Of course, inother advantageous embodiments, structural members 612 may be insertedinto foam 604 after foam 604 has been shaped and is ready for compositematerial 602 to be laid up on foam 604. Typically, this type of lay upis used to manufacture a hat composite stringer, which is a stringerwith acute angles in a trapezoidal shape.

Turning now to FIG. 7, a diagram illustrating an example lay up ofcomposite materials on an outside mold line tool for a compositestringer is depicted in accordance with an advantageous embodiment. Inthis example, composite stringer 700 includes foam 702 and compositematerial 704. Foam 702 is placed on fuselage skin 706. Compositematerial 704 is placed or laid up over foam 702 and fuselage skin 706.As in the other example, foam 702 includes structural members 708. Thesecomponents form composite stringer 700 in a pre-cured state on outsidemold line tool 710. In this example, bag 712 is placed over compositestringer 700 for curing composite stringer 700.

With reference now to FIG. 8, a cross-sectional view of a foam-filledstringer with structural members is depicted in accordance with anadvantageous embodiment. In this example, composite stringer 800 hascomposite material 802, foam 804, and structural members 806. In thisexample, structural members 806 may take the form of pins having thesame orientation in the direction of arrow 808. Structural members 806may have an orientation to resist a number of loads. This number ofloads may occur during curing of composite stringer 800.

Further, this resistance to loads also may be for loads that may beapplied to composite stringer 800 after installation or attachment toanother component. In this example, the number of orientations forstructural members 806 is a single angle that is substantially normal toskin ply 810. In this example, structural members 806 may be around 90degrees to surface 812 of skin ply 810.

Further, with the use of structural members 806, walls 814 of compositestringer 800 may be manufactured with less thickness. For example, oneless ply of composite material may be used within walls 814. Structuralmembers 806 provide a capability to resist a number of loads that may beapplied to walls 814 of composite stringer 800.

With reference now to FIG. 9, a diagram illustrating a cross-sectionalview of a composite stringer is depicted in accordance with anadvantageous embodiment. In this example, a portion of compositestringer is taken along lines 9-9 in FIG. 8. In this view, a density forstructural members 806 within foam 804 may be seen. Structural members806 are distributed evenly within foam 804 in these examples. Of course,other types of distributions and densities may be used depending on theparticular implementation.

With reference now to FIG. 10, a diagram of a composite stringer isdepicted in accordance with an advantageous embodiment. In this example,composite stringer 1000 is formed from composite materials 1002, foam1004, and structural members 1006. In this example, structural members1006 may take the form of pins having a number of orientations. In thisexample, two orientations are present for structural members 1006. Theseorientations are perpendicular to each other and may form athree-dimensional grid-type structure.

Structural members 1006 have orientation 1008 and orientation 1010.Orientation 1008 is substantially parallel to skin ply 1012, whileorientation 1010 is substantially perpendicular to skin ply 1012.

With reference now to FIG. 11, a diagram illustrating a compositestringer is depicted in accordance with an advantageous embodiment. Inthis illustrative example, composite stringer 1100 has compositematerials 1102, foam 1104, and structural members 1106. Structuralmembers 1106 have two orientations. Structural members 1106 haveorientation 1108 and orientation 1110. These orientations aresubstantially perpendicular to each other but may have an angle ofaround 45 degrees and around 135 degrees to surface 1112 to skin ply1114.

The illustrations of cross sections for composite stringers in FIGS.8-11 have been provided for illustrating some configurations forcomposite stringers in accordance with advantageous embodiments. Ofcourse, other configurations may be used depending on the particularimplementation. For example, other numbers of orientations forstructural members may be used. For example, three or four orientationsmay be used instead of one or two orientations for structural members.

For example, the measurement of the orientations for structural membersmay be based on other references than a skin ply or bottom surface forthe composite stringer. Also, different densities for structural membersmay be employed. For example, densities for the structural members maybe greater at areas of the composite stringer where greater loads may beanticipated for the composite stringer.

With reference now to FIG. 12, a flowchart of a process formanufacturing a composite part is depicted in accordance with anadvantageous embodiment. The process illustrated in FIG. 12 may beimplemented using the different tools illustrated in FIG. 5.

The process begins by forming a foam core having a plurality ofstructural members (operation 1200). The plurality of structural membershas a number of orientations to resist a number of loads. The processthen forms a composite part with a channel in which the foam core withthe structural members is located (operation 1202), with the processterminating thereafter.

Turning now to FIG. 13, a flowchart of a process for manufacturing acomposite stringer with a foam core is depicted in accordance with anadvantageous embodiment. The process illustrated in FIG. 13 may beimplemented using tools depicted in FIG. 5.

The process begins by forming plies of composite material (operation1300). This operation may involve cutting plies of composite tape and/orfabric, stacking the plies together, and vacuum compacting the compositematerial to form a flat charge. Thereafter, the composite material isformed into a stringer shape (operation 1302). Operation 1302 mayinvolve using a dye or press to shape the flat charge into a stringershape.

The process then prepares the foam with structural members (operation1304). Operation 1304 may be used to create a foam core for thecomposite stringer. Structural members are placed into the foam inoperation 1304. In other instances, the foam may be formed around thestructural members.

Next, a determination is made as to the type of tool being used(operation 1306). If the tool is an outside mold line tool, the processplaces the foam onto skin plies (operation 1308). Thereafter, the foamis draped with the composite material (operation 1310).

The process then cures the composite stringer assembly (operation 1312).This curing operation also may include compacting the assembly with avacuum in the autoclave/oven, with the process terminating thereafter.

With reference again to operation 1306, if the type of tool is an insidemold line tool, the process places the composite material and the foaminto the mold (operation 1316). Next, the process places skin plies overthe composite material (operation 1318), with the process thenproceeding to operation 1312 as described above.

The composite stringer manufactured using this process may be used withvarious aircraft parts to provide for increased stiffening. Further, thecomposite stringer also may provide for noise and vibration dampeningfor various components. The composite stringer also may reduce and/orprevent liquids from travelling into the stringer or through thestringer.

The flowcharts and block diagrams in the different depicted embodimentsillustrate the architecture, functionality, and operation of somepossible implementations of apparatus, methods, and computer programproducts. In this regard, each block in the flowchart or block diagramsmay represent a module, segment, or portion of computer usable orreadable program code, which comprises one or more executableinstructions for implementing the specified function or functions.

One or more of the different blocks also may represent operationsperformed by a human operator, tool, or some other suitable actor. Insome alternative implementations, the function or functions noted in theblock may occur out of the order noted in the figures. For example, insome cases, two blocks shown in succession may be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. Also, in someadvantageous embodiments, other blocks may be used in addition to theillustrative blocks, while some blocks may be optional.

Thus, the different advantageous embodiments provide a method andapparatus for forming composite parts. In the different advantageousembodiments, a foam core having a plurality of structural members isformed. This plurality of structural members has a number oforientations to resist a number of loads. The composite part is formedwith a channel in which the foam core is located.

The composite stringer, in the different advantageous embodiments, maybe manufactured using a lighter weight foam without having the foamcollapse during a curing process. The use of structural members providesa resistance to a number of loads that may be applied during the curingprocess. As a result, the weight of composite stringers may be reducedthrough the use of lighter weight foams.

Further, with the different advantageous embodiments, the compositestringers may be capable of resisting loads that may be applied to thecomposite stringers during use. The composite stringers also provide acapability to block liquids as well as provide for sound and vibrationdampening. Further, with the use of structural members, the thickness ofthe walls of the composite stringers may be made thinner to reduce theweight of the composite stringers.

The description of the different advantageous embodiments has beenpresented for purposes of illustration and description, and it is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Although the different advantageousembodiments have been described with respect to aircraft, otheradvantageous embodiments may be applied to other types of objects.

For example, without limitation, other advantageous embodiments may beapplied to a mobile platform, a stationary platform, a land-basedstructure, an aquatic-based structure, a space-based structure, and/orsome other suitable object. More specifically, the differentadvantageous embodiments may be applied to, for example, withoutlimitation, a submarine, a bus, a personnel carrier, a tank, a train, anautomobile, a spacecraft, a space station, a satellite, a surface ship,a power plant, a dam, a manufacturing facility, a building, and/or someother suitable object.

Further, different advantageous embodiments may provide differentadvantages as compared to other advantageous embodiments. The embodimentor embodiments selected are chosen and described in order to bestexplain the principles of the embodiments, the practical application,and to enable others of ordinary skill in the art to understand thedisclosure for various embodiments with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A method for manufacturing a composite stringer,the method comprising: placing a plurality of structural members withina foam, the plurality of structural members comprising at least one of anumber of pins, a number of tubes, and a number of rods; laying up acomposite material and the foam with the plurality of structural memberswithin the foam onto a tool in the form of a stringer, wherein theplurality of structural members has at least a first orientation and asecond orientation, the first orientation and the second orientationbeing different from each other, the plurality of structural membersconfigured to resist a number of loads on the stringer including atleast compressive loads; placing the foam and the composite materialonto a skin ply such that the plurality of structural members within thefoam do not substantially pierce the skin ply; wherein the structuralmembers extend from the skin ply to a first and a second wall of thecomposite stringer and wherein the structural members are positionedsubstantially within the foam; and curing the composite material, thefoam in the form of the stringer, and the plurality of structuralmembers to form the composite stringer.
 2. The method of claim 1 furthercomprising: placing the plurality of structural members within the foam;shaping the foam for the composite stringer with the plurality ofstructural members within the foam.
 3. The method of claim 1, whereinthe laying up step comprises: laying up the composite material onto aninside mold line; and placing the foam onto the composite material. 4.The method of claim 3, wherein the laying up step further comprises:placing a skin ply over the foam and the composite material.
 5. Themethod of claim 4 wherein the laying up step is performed using anoutside mold line.
 6. The method of claim 1, wherein the compositestringer has a shape selected from one of a trapezoid shape, a hatshape, a solid shape, and a hollow shape.
 7. The method of claim 1,wherein the plurality of structural members is comprised of a materialselected from one of aluminum, steel, carbon-reinforced material,graphite-reinforced material, titanium, a metal alloy, and a ceramicmaterial.
 8. The method of claim 1, wherein the plurality of structuralmembers has a first density in a first area and a second density in asecond area.
 9. The method of claim 1, wherein the composite stringer islocated in an aircraft.
 10. The method of claim 1, wherein the firstorientation and the second orientation are selected so as to besubstantially normal to each other.
 11. A method for forming a compositepart, the method comprising: laying up a composite material and a foamcore onto a tool in a form of the composite part, the foam core having aplurality of structural members, wherein the plurality of structuralmembers has at least a first orientation and a second orientation, thefirst orientation and the second orientation being different from eachother, the plurality of structural members configured to resist a numberof loads including at least compressive forces on the composite part,the plurality of structural members comprising at least one of a numberof pins, a number of tubes, and a number of rods; placing the foam coreand the composite material onto a skin ply; curing the compositematerial and the foam core in the form of the composite part such thatthe plurality of structural members do not substantially pierce the skinply; wherein the structural members extend from the skin ply to a firstand a second wall of the composite part stringer and wherein thestructural members are positioned substantially within the foam; andforming the composite part with a channel in which the foam core islocated.
 12. The method of claim 11, wherein the laying up stepcomprises: laying up the composite material onto an inside mold line;and placing the foam core onto the composite material.
 13. The method ofclaim 11, wherein the plurality of structural members has a firstdensity in a first area and a second density in a second area, the firstdensity and second density being different.
 14. The method of claim 11,wherein the composite part is a composite stringer.
 15. The method ofclaim 14, wherein the composite stringer has a shape selected from oneof a trapezoid shape, a hat shape, a solid shape, and a hollow shape.16. The method of claim 11, wherein the plurality of structural membersis comprised of a material selected from one of aluminum, steel,carbon-reinforced material, graphite-reinforced material, titanium, ametal alloy, and a ceramic material.
 17. The method of claim 11, whereinthe first orientation and the second orientation are selected so as tobe substantially normal to each other.
 18. A method for manufacturing aplurality of composite stringers, the method comprising: laying upcomposite material and foam with a plurality of z-pins within the foamonto a plurality of tools to form a plurality of composite stringers,wherein the plurality of z-pins has at least a first orientation, theplurality of z-pins configured to resist a number of loads includingcompressive loads on the composite stringers, and the plurality ofz-pins comprising at least one of a number of pins, a number of tubes,and a number of rods; placing the plurality of composite stringers on asingle tool; placing a skin ply over the plurality of compositestringers to form a structure; wherein the plurality of z-pins extendsfrom the skin ply to a first and a second wall of the compositestringers and wherein the structural members are positionedsubstantially within the foam; and curing the structure such that theplurality of z-pins do not substantially extend past the first and thesecond wall of the composite stringer.